The present invention relates to a process for preparing polyolefins. More particularly, the present invention is concerned with a process for preparing polyolefins exhibiting better particle properties with increase of an average particle diameter, which process is capable of greatly increasing the polymer yield per solids and that per transition metal, thereby permitting the omission of the step of removing catalyst remaining in the resulting polymer, further capable of increasing the bulk density of the polymer and decreasing a fine particulate portion of the polymer.
Heretofore, in this technical field there have been known many catalysts comprising inorganic magnesium solids as carriers such as magnesium halide, magnesium oxide and magnesium hydroxide and a transition metal compound such as a titanium compound or a vanadium compound supported on the carriers. However, the polyolefins obtained in the prior art are generally low in bulk density, relatively small in average particle diameter and generally wide in particle size distribution so contain a large proportion of fine particles. For this reason, improvement has keenly been desired from the standpoint of productivity and polymer handling. Besides, when these powdery polymers are subjected to forming, there arise problems such as dusting and lowering of the forming efficiency. So there has been a keen desire for the foregoing increase of bulk density and decrease of the fine particulate portion. Further, still further improvements are considered necessary in order to satisfy the recent keen desire for omitting the pelletizing step and using a powdery polymer directly in a processing machine.
The present inventors have previously found a novel catalyst component with the above drawbacks remedied and already filed patent applications thereon (see Japanese Patent Publication Nos. 11651/1989 and 12289/1989 and Japanese Patent Laid-Open Nos. 149605/1985, 32105/1987 and 207306/1987). The use of this catalyst component can afford a polymer having a high bulk density and a large average particle diameter. However, a further improvement has been considered necessary for omitting the pelletizing step and using a powdery polymer directly in a processing machine.
It is the object of the present invention to remedy the above-mentioned drawbacks and obtain in extremely high activity a polymer having a high bulk density, a narrow particle size distribution, an extremely proportion of fine particles, and superior in fluidity.